1. Field of the Invention
The present invention relates to a flat fluorescent lamp and a liquid crystal display device. More particularly, the present invention relates to a flat fluorescent lamp that can provide a planar light source with high uniformity and a liquid crystal display device having the aforementioned flat fluorescent lamp.
2. Description of the Related Art
With the rapid progress in display techniques, liquid crystal display devices have been massively deployed as the display screens of consumer electronic products including mobile phones, notebook computers, personal computers and personal digital assistants. However, the liquid crystal display panel of a liquid crystal display device has no light-emitting capability. Hence, there is a need to install a back light module underneath the liquid crystal display panel to provide all the light needed for the display function. At present, the principle types of back light module in the market include the flat fluorescent lamp (FFL), the cold cathode fluorescent lamp (CCFL) and the light-emitting diode. Among these three types of back light modules, the flat fluorescent lamp is more commonly used in the liquid crystal display device because it is cheaper to produce and occupies a smaller space.
FIG. 1 is a schematic cross-sectional view showing part of a conventional planar fluorescent lamp. As shown in FIG. 1, the conventional flat fluorescent lamp 100 comprises a top substrate 110 and a bottom substrate 120 pairing together. A discharge space is formed between the top substrate 110 and the bottom substrate 120 and the discharge space is filled with a discharge gas 130. A set of electrodes 140 is disposed on the bottom substrate 120 and a dielectric layer 150 is disposed over the set of electrodes 140 to protect the set of electrodes 140. In addition, a fluorescent material 160 is coated over the inner sidewall of the top substrate 110 and the bottom substrate 120 and the outer wall of the dielectric layer 150.
The flat fluorescent lamp 100 is driven by applying a driving voltage to the set of electrodes 140 to produce a discharge electric field E. The discharge electric field E will ionize the discharge gas 130 to produce plasma. As the excited electrons in the ions of the plasma return to a ground state, ultra-violet rays are simultaneously produced. When the ultra-violet rays from the plasma shine on the fluorescent material 160, the fluorescent material 160 will be excited to emit visible light.
At present, most flat fluorescent lamps use a driving system capable of providing a controlled local discharge, for example, a design having a plurality of protruding points on an electrode for producing a multiple of point discharges. However, such local discharge can easily lead to the production of a higher intensity beam in a local area. Hence, a regular pattern of light/dark streaks will appear. Ultimately, the degree of uniformity of the light intensity across the flat fluorescent lamp will be reduced.